Low Frequency Bilateral Communication Over Distributed Power Lines

ABSTRACT

A system and method for providing full-duplex data communications between an electric power distribution station and a power consumer via the power distribution line providing electric power is provided. A first information transmitter, coupled to the power distribution circuit, provides first information signals concurrently with the power signal to the power consumer via the power distribution line. A first information receiver, coupled to a power consumer device powered by the electrical power signal, receives the first information signals via the electric power distribution line. A second information transmitter coupled to the power consumer device provides second information signals concurrently with the electrical power signal. A second information receiver, coupled to the power distribution circuit, receives the second information signals via the electric power distribution line. The information signals transmitted on the power distribution line can be transmitted at a frequency lower than the frequency of the transmitted power signal.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/068,496, filed Feb. 28, 2005, entitled “Low Frequency BilateralCommunication Over Distributed Power Lines”, which issued on ______ asU.S. Pat. No. ______, which is a continuation of U.S. application Ser.No. 10/649,061, filed Aug. 27, 2003, which is a continuation of U.S.application Ser. No. 10/208,431, filed Jul. 29, 2002, which is acontinuation of U.S. application Ser. No. 09/723,090, filed Nov. 27,2000, which is a continuation of U.S. application Ser. No. 08/933,745,filed Sep. 23, 1997, which issued on Nov. 28, 2000 as U.S. Pat. No.6,154,488, which applications are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to data communications, and moreparticularly to a system and method for providing full-duplex datacommunications between an electric power distribution station and apower consumer, via the same power distribution line that provideselectric power to the power consumer, at frequencies at or below thefrequency of the electric power signal.

BACKGROUND OF THE INVENTION

As is true with most companies, utility companies are striving to reduceoverhead costs, while providing more convenience to customers. Forexample, electric companies are migrating from costly and time-consumingmanual methods of determining the amount of power consumed by customersof the power company. Traditionally, a person periodically came to thecustomer's home, and requested entry to read the consumer power usagefrom a power meter. This type of process was costly, slow, and intrusiveto their customers. In order to alleviate some of the problemsassociated with the traditional approach, other approaches have beenemployed, including wireless and modem transmission of power usageamount.

However, it is often the case that there is information that the powercompany may want to provide to their customers. While generalinformation, such as the current price of power, price increases, etc.may be made available to customers via mail or telephone, it is againcostly, time consuming, and intrusive.

Furthermore, many power companies provide customers with cost discountsif the customer agrees to allow the power company to temporarily adjustor terminate their power consumption for certain “non-essential”power-consuming devices (e.g., air conditioners, water heaters, swimmingpool heaters, etc.) during peak operation. This is commonly referred toas “load control” or “load limiting”. This allows the power company tolimit the peak power consumption when necessary. Otherwise, the powercompany may have to purchase more expensive power from alternativesources to meet its peak load demand. A one-way wireless pagertechnology could be used to service the peak load in this manner. Forexample, a power company could send a digital message via one-way pagertechnology to a particular geographic area including a number ofcustomers who have agreed to allow the power company to alter theirpower during peak power periods. The pager at the destination wouldreceive a digital word indicating that the power should be temporarilyterminated. Because the communication would be unilateral, no signalacknowledge would be provided, and there would be no manner, short of atrial-and-error method, to determine whether the customer's power tothese appliances was ever suspended. Furthermore, customers could alsotamper with the pager systems to avoid having their power temporarilyterminated, while continuing to obtain the cost discount.

Therefore, it would be desirable to allow information to be providedfrom the power company to any one or more of their power consumers,while allowing for receipt acknowledgment and other signals. It wouldalso be desirable to utilize power distribution line to provide suchinformation, in order to avoid new wiring and its associated costs andinstallation time requirements. Utilizing the existing powerdistribution line would also minimize customer tampering during loadcontrol periods, as tampering with or severing the control line would betantamount to eliminating their own source of power because the power istransmitted on the same conductor. The use of frequencies having a verylong wavelength would also be desirable, to minimize the need for signalrepeaters, and to minimize harmonic effects and reduce the overall noiseon the power line which can adversely affect electronic devices such ascomputers.

While the prior art does not provide the aforementioned functionality,the present invention provides a solution to these and othershortcomings of the prior art, and further provides additionaladvantages over the prior art.

SUMMARY OF THE INVENTION

Generally, the present invention relates to a system and method forproviding full-duplex data communications between an electric powerdistribution station and a power consumer via the same powerdistribution line that provides electric power to the power consumer.

In accordance with one embodiment of the invention, a full-duplexcommunications system for transmitting information is provided. A powerdistribution circuit is coupled to an electric power distribution lineto transmit an electrical power signal to a power consumer. A firstinformation transmitter, which is coupled to the power distributioncircuit, provides first information signals concurrently with theelectrical power signal to the power consumer via the electric powerdistribution line. A first information receiver, coupled to a powerconsumer device powered by the electrical power signal, receives thefirst information signals via the electric power distribution line. Asecond information transmitter coupled to the power consumer deviceprovides second information signals concurrently with the electricalpower signal via the electric power distribution line. A secondinformation receiver, coupled to the power distribution circuit,receives the second information signals via the electric powerdistribution line. This configuration allows for full-duplexcommunication between the power distribution circuit and the powerconsumer via the electric power distribution line.

In accordance with another embodiment of the invention, a full-duplexcommunications system for disseminating information from a powerdistribution station to a plurality of power consumer sites via theelectric power distribution line providing power to the plurality ofpower consumer sites is provided. An information transmitter at thepower distribution circuit provides information signals via the powerdistribution line to the plurality of power consumer sites while alsoproviding the power consumer sites with electric power. Each of thepower consumer sites includes at least one information receiver which iscoupled to a power consuming device which also receives the informationsignals. Each consumer site also includes a consumer informationtransmitter to provide consumer information to the power distributionstation via the power distribution line, which is received at the powerdistribution circuit by a consumer information receiver. Thisconfiguration provides for full-duplex communication between a utilitypower source and each of the power consumer sites, without the need foradditional wiring.

In accordance with yet another embodiment of the invention, acommunications system for transmitting information from a utility powerdistribution node to a power consumer via an electric power distributionline is provided. A transmitting circuit at the power distribution nodetransmits an information signal via the power distribution line at afrequency less than the frequency at which the power is transmitted onthe power distribution line. This low frequency signal is received by areceiving circuit at a customer site via the power distribution line. Inone embodiment of the invention, a low frequency modulating circuitsuperimposes the information signal onto the electric power signal whichprovides power to the consumer.

In accordance with another embodiment of the invention, a signaltransmission device transmits information signals from a utility powerdistribution node to a power consumer via a power distribution line. Thesignal transmission device includes an information signal modulatingcircuit to superimpose an information signal on the power signal. Thefrequency of the information signal generated has a frequency less thanthe frequency of the power signal. The modulating circuit includes azero-crossover sense circuit to determine the approximate zero-crossoverpoints of the power signal. A signal inversion circuit inverts the phaseof every nth half-period of the power signal between successivezero-crossover points. By altering the phases of the power signal, thecontrol signal can be superimposed onto it, wherein consecutive positivephases of the altered power signal correspond to a first logic state(e.g., a “high” logic level) of the information signal, and consecutivenegative phases of the altered power signal correspond to a second logicstate (e.g., a “low” logic level) of the information signal. Signaldriving circuitry concurrently drives the altered power signal, and theelectric power, to the power consumer via the power distribution line.

In accordance with another aspect of the invention, a communicationmethod for communicating between an electric power provider and anelectric power consumer via an electric power distribution line isprovided. A power signal is provided to the power consumer via theelectric power distribution line at a predetermined power signalfrequency. A control signal, corresponding to the control information,is concurrently transmitted to the power consumer via the electric powerdistribution line. The control signal is transmitted at a frequency lessthan the frequency of the power signal. The control information can beused to manipulate the operation of the consumer devices at the powerconsumer site.

The above summary of the present invention is not intended to describeeach illustrated embodiment or every implementation of the presentinvention. The figures and the detailed description which follow moreparticularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one link of an electric distribution systemdistributing power between a utility substation and a customer device atthe power consumer's site;

FIG. 2 is a block diagram of a power distribution system implementing aninformation transmitter in accordance with the present invention;

FIG. 3 is block diagram illustrating one embodiment of the connection ofthe power generation and control information transmitter at the utilitysubstation;

FIG. 4 is a block diagram of one embodiment of a control informationtransmitter in accordance with the present invention;

FIG. 5 is a block diagram of a zero-crossover sense circuit inaccordance with one embodiment of the present invention;

FIG. 6 is a waveform diagram illustrating the anticipation of thezero-crossover point;

FIG. 7 is a diagram illustrating the function of the zero-crossoversynchronization in accordance with one embodiment of the presentinvention;

FIG. 8 is a schematic diagram of a power transistor circuit inaccordance with one embodiment of the invention;

FIG. 9 is a waveform diagram illustrating one embodiment in which a lowfrequency control signal is derived using the frequency of the powersignal as a carrier signal;

FIG. 10 is a functional illustration of one embodiment of a high voltageprotection unit in accordance with the present invention; and

FIG. 11 is a diagram illustrating one embodiment of the control signalprotocol of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 is a block diagram of one link of an electric distribution system100 distributing power between a utility substation and a customerdevice at the power consumer's site. An electric distribution system, ordistribution plant as it is sometimes referred to, is all of that partof an electric power system between the bulk power source or sources andthe consumer service switches. The bulk power sources are located in ornear the load area to be served by the distribution system, and may beeither generating stations or power substations supplied overtransmission lines. Subtransmission circuits extend from the bulk powersource or sources to the various distribution substations located in theload area. The subtransmission circuits typically consist of undergroundcable, aerial cable, or overhead open-wire conductors carried on poles,or some combination of them.

Each distribution substation normally serves its own load area, which isa subdivision of the area served by the distribution system. At thedistribution substation the subtransmission voltage is reduced forgeneral distribution throughout the area. The substations consists ofone or more power-transformer banks together with the necessary voltageregulating equipment, buses, and switchgear. Distribution transformersare ordinarily connected to the distribution transformer, which serve tostep-down from the distribution voltage to the utilization voltage.These step-down transformers, often referred to as pole transformers,supply a consumer or group of consumers over a secondary circuit. Eachconsumer is connected to the secondary circuit through its service leadsand meter.

The utility substation 102 shown in FIG. 1 represents any powerdistribution point in an electric distribution system. Therefore, in asmall distribution system, the utility substation 102 may represent theoriginating bulk power source, or may represent a distributionsubstation further down the distribution chain. The utility substation102 provides power to a customer device 104 at a power consumer site viaa power distribution line 106. The power distribution line 106 may becoupled to one or more step-down transformers prior to reaching thecustomer site. The power distribution line provides the power necessaryto operate electrical devices, such as the customer device 104, at thecustomer site.

For a variety of reasons, it may be desirable to communicate informationfrom the utility substation 102 to one or more customer devices 104 at aparticular customer site. For example, it may be desirable to control ormonitor a meter reading device, which is installed at a customer site todetermine the power consumption at that customer site. Controlinformation could provide the ability to control or alter the operationof the meter reading device. Furthermore, utility companies oftenprovide a customer with a power rate discount if the customer agrees toallow for a temporary adjustment of their consumption. For example, apower company may provide a customer with a rate discount where thecustomer agrees to allow the power company to temporarily adjust orterminate their power consumption for certain nonessential powerconsuming devices, such as water heaters, swimming pool heaters, airconditioners, etc. during peak operation. This allows the utilitycompany to limit the peak power consumption when necessary, hereinafterreferred to as “load control”.

Other more general information, which is not necessarily to “control”customer devices, can also be provided via the power distribution lines.These general information signals are transmitted in the same manner assignals intended to control a customer device. Such general informationsignals include information to display or store the price of power atthe customer site, the date and time, the temperature or otherinformation capable of being received and translated at the customersite. For example, the time displayed on an electronic device at thecustomer site could be periodically adjusted to display an accurate timeas transmitted by the utility station.

The present invention therefore allows control signals and generalinformation signals to be sent to the particular customer device via thepower distribution line 106 to control customer devices and provide moregeneral information to the customer. Information from the customerdevice may also be sent via the power distribution line to the utilitysubstation 102, thereby creating a two-way control informationcommunication link via the power distribution line 106. Theaforementioned examples of control signal applications where controlsignals (and/or general information signals) are provided by the utilitysubstation to a customer site are merely representative of the varioususes that such control signals provide. Therefore, the examples providedthroughout the application are illustrative in nature, as the inventionis not limited to any particular control signal use.

In order to provide control information at the utility substation 102, atransmitter 108 is used to drive the control signals along the powerdistribution line 106 in the direction represented by the arrow 110. Areceiver 112 at the customer device is configured to recognize thecontrol signals transmitted by the control information transmitter 108.Similarly, the utility substation 102 may be equipped with aninformation receiver 114 to receive information, such as a powerconsumption reading, from a transmitter 116 at the customer device 104in the direction represented by arrow 118.

The control information communications link 100 shown in FIG. 1therefore provides a full-duplex communications link between the utilitysubstation 102 and the customer site. Full-duplex in this sense refersto simultaneous communications in both directions, although theinformation sent in one direction may travel at a speed different thanthat of the information provided in the opposite direction. Thisfull-duplex communication link via the power distribution line 106provides for reliable transmission of control information, without theneed for additional wiring, thereby minimizing cost and increasing dataintegrity.

The full-duplex communication link 100 is designed for the transfer ofcontrol information at a frequency at or below the frequency at whichthe power is being distributed on the power distribution line 106. Suchlow frequency control signals provides for longer transmission links,and there is little chance that the data will interfere with theelectrical power transmission. Furthermore, a low frequency signal canpass through downstream transformers and capacitors with minimal signaldegradation, and without the aid of additional equipment such asrepeaters.

Data analyzation using low frequency control signals over a period oftime can provide a great deal of valuable information. For example, inload control situations where a power consumer has agreed to havenonessential power consuming devices regulated by the power company,each request by the power company to adjust or temporarily terminate thepower to the consumer can be stored and compared to an acknowledgmentreceived at a later time. If it is determined that power consumption atthe customer site decreased over a period of time and/or over a numberof occurrences of request/acknowledgment events, the power adjusting orterminating request was likely successful. On the other hand, if thepeak power consumption did not decrease during these times, an equipmentfailure may have occurred, or the customer may have tampered with thecontrol signal receiver at the customer device 104. Statisticalinformation gathered over time can protect the utility companies fromproviding a discount to a power consumer where it is unwarranted.

Referring now to FIG. 2, a block diagram of a power distribution system200 implementing an information transmitter in accordance with thepresent invention is provided. A utility central office 202 provides thebulk power, and a transmit control signal, to the utility substation 204including the control information transmitter 206. As can be seen by theexample of FIG. 2, the control information transmitter cansimultaneously transmit control information via the power distributionlines 208 to multiple customer devices residing in multiple customersites. The control information can pass through transformers 210, andultimately to a particular customer site 212. A plurality of customersites may be serviced by a particular transformer 210, as illustrated bycustomer site n 214. Furthermore, a customer site such as site 216 mayinclude a plurality of different customer devices 218. The transfer ofcontrol information from a utility substation information transmitter206 to a great number of customer sites is very useful, yet costeffective.

FIG. 3 is block diagram illustrating one embodiment of the connection ofthe power generation and control information transmitter at the utilitysubstation 300. The substation 300 typically includes a main transformer302 which provides 3-phase power to the customer site 304. Phases A, Band C on lines 306, 308 and 310 respectfully are transmitted to thereceiver 312 at the customer site 304. In order to induce the controlinformation onto the three phases 306, 308 and 310 of the powerdistribution line 314, the control information transmitter 316 generatesa voltage on the secondary windings 318 of the transformer 320 onto theprimary windings 322 according to the transformer 320 turns ratio. Thecustomer site 304 is equipped with receivers 312 at the customer devicesso that the control information can be extracted from the power signal.In one embodiment of the present invention, the receiver is a digitalsignal processing (DSP) device requiring no analog components. DSPtechnology used to extract such a control signal is readily available tothose skilled in the art. The customer site 304 also includes transmitcircuitry 313, which allows information, such as power consumption usagemeasured by a meter, to be sent back to the utility substation 300 viathe power distribution line 314.

Transmit control circuitry at the utility central office is used toprovide a bitstream of binary data, shown as the transmit control signalon line 315, to assist in modulating the control signal at the controlinformation transmitter 316. The transmit control circuitry at theutility central office may include a modem connection to a remote sitein order to receive the actual information which is to be converted intothe control signal. The transmit control signal is a bitstream whichcorresponds to the actual information to be converted into the controlsignal. For example, the bitstream can include binary indications of themodulation points in a frequency modulated system, so that a binary “1”corresponds to a first frequency, and a binary “0” corresponds to asecond frequency in the frequency modulated system. The transmit controlsignal is described in further detail in connection with FIG. 9.

The control information transmitter 316 is coupled in series with theneutral line 324 of the main transformer 302. Therefore, the controlsignal voltage generated by the control information transmitter 316causes the voltage on the neutral line to correspond to the controlsignal generated. The control signal is also applied to the three phasesof the power distribution line 314. Therefore, while the voltage on eachof the phases of the power distribution line 314 may go to a highervoltage than where only the power signal were present on the line, thevoltage on the neutral line 324 is similarly modulated such that thevoltage at each of the phases does not change with respect to thevoltage on the neutral line 324.

Because the control information transmitter 316 is coupled in serieswith the neutral line 324, an open-circuited condition in the controlinformation transmitter 316 could result in an excessively large voltagebeing present at the customer site 304. In order to address thissituation, at least one high voltage protection unit 326 is coupledbetween the neutral line 324 and earth ground. Other voltage protectionalso resides in the control information transmitter 316. Theseprotection modules, as well as the high voltage protection circuit 326,will be described in greater detail in connection with the descriptionscorresponding to FIGS. 4 and 10.

Referring now to FIG. 4, a block diagram is provided of one embodimentof a control information transmitter 400 in accordance with the presentinvention. The control information transmitter 400 is coupled in serieswith the power line at the neutral line 402, rather than in parallel.This causes the reference value to be changed from reference ground to areference that changes as the control signal changes. While atransmitter could transmit information in parallel across the secondarywindings 404, the very low impedance of the secondary windings 404results in a large power dissipation. By coupling the controlinformation transmitter 400 in series with the neutral line 402, onlythe unbalanced current in the neutral line 402 is dissipated. In aperfectly balanced circuit, no current would exist at all. However,typical circuits are not perfectly balanced, and the unbalanced currentis often in the range of 120 amps.

The control signal is consequently injected in the neutral line 402 ofthe power distribution, line due to its in-series connection. Thissignal can have various peak or RMS voltage values, and in oneembodiment of the invention is set to a value in the range of 20 voltsto 120 volts utilizing phase modulation to generate the control signal.The signal is generated by the electronics module 406, and is passedthrough the protection module 408 onto the secondary windings 404 viathe secondary winding power 1 line 410 and a secondary winding power 2line 412.

The protection module 408 provides overvoltage protection for differentvoltage levels (i.e., different voltage thresholds) and at differentspeeds than the overvoltage protection provided by the high voltageprotection unit 326 shown in FIG. 3. The protection module 408 provideshigher speed solid-state protection to detect excessive voltages, butdoes so for voltages lower than the potentially very high voltagesdetected by the high voltage protection unit 326 of FIG. 3. For example,in one embodiment of the invention, the protection module 408 includescapacitance banks (not shown) coupled between the power 1 410 and power2 412 lines, which can respond on the order of nanoseconds, whichimpedes voltage rise times by shunting voltage transients to ground.Large silicon-controlled rectifiers (SCRs) coupled between the power 1410 and power 2 412 lines, which can respond on the order ofmicroseconds, are used to switch voltages to ground which exceed apredetermined voltage quantity. SCRs typically refer to a three-leaddevice which substantially becomes a short-circuit when its gate lead istriggered by a special voltage level, and returns to an open circuitwhen its gate lead is returned to a low voltage. Large solid-staterelays can also be used across the power 1 and power 2 lines 410, 412.High voltage protection, such as the high voltage protection unit 326 ofFIG. 3, is described in greater detail in connection with FIG. 10.

The electronics module 406 generates the low-frequency control signalcorresponding to the desired control function to be performed. In oneembodiment of the invention, the electronics module 406 includescrossover sense circuitry 414, crossover synchronization circuit 416,signal drivers 418, 420, 422, 424, and power switching transistors 426,428, 430, 432. The crossover sense circuit 414 detects approximatelywhen a carrier signal, such as the power signal transmitted on the powerdistribution line, crosses the zero-voltage point. This circuit is usedwhen the control signal is to be modulated onto the power signal itself,and modulating the control signal during near-zero crossover pointsminimizes harmonics and other noise on the line. The crossover sensecircuitry 414 is described in greater detail in connection with thedescription corresponding to FIG. 5.

The electronics module 406 also includes crossover synchronizationcircuitry 416 which receives a bitstream of information from thetransmit control circuit at the utility central office which correspondsto the actual information to be converted into the control signal. Fromthis transmit control signal on line 417, the crossover synchronizeblock 416 manipulates the on/off operation of the power switchingtransistors 426, 428, 430, 432, and does so at a time dictated by thecrossover sense 414 output.

FIG. 5 is a block diagram of a zero-crossover sense circuit 500 inaccordance with one embodiment of the present invention. Because thecontrol signals are transmitted on a physical transmission medium commonto the transmission of the power being provided to a power consumer, itmay be advantageous to use the power signal itself as a carrier wave forthe control signal. In one embodiment of the invention, a low frequencycontrol signal is modulated onto the 60 Hz power signal transmitted tothe power consumer. Furthermore, the control signal is transmitted at afrequency lower than that of the power signal, because of the desirabletransmission qualities of low frequency transmission. In order toeffectively modulate a low frequency signal on the power signal, thepresent invention provides a zero-crossover sense circuit 500, whichanticipates the zero-crossover point of the 60 Hz power signal,therefore providing for state transitions of the low frequency controlsignal at the approximate zero-crossing point. This “near zero-crossswitching” minimizes harmonics and other noise on the line, so as toavoid affecting a customer's electrical devices, such as computers,phone lines, and the like.

The voltage applied to the primary windings 322 of the transformer 320are induced onto the center-tapped secondary windings 318, as was shownin FIG. 3. This causes a secondary winding power 1 line 502 and asecondary winding power 2 line 504 of FIG. 5 to each provide a signal ofequal frequency to the voltage on the primary windings. Each has a peakvoltage equal to one-half of the peak primary voltage, and is 180degrees phase-shifted from the other, due to the characteristics of thecenter-tapped transformer. Although the invention is capable ofoperation at various RMS voltages and frequencies, a 120 volt RMSvoltage at 60 Hz in the primary windings will be assumed for purposes ofthe ensuing description. Therefore, the secondary winding power 1 line502 and the secondary winding power 2 line 504 are 60 volt RMS signalstransmitted at 60 Hz.

The secondary winding power signals on lines 502 and 504 are appliedacross a voltage dividing circuit, which in FIG. 5 is represented by aseries of resistances R1-A 506, R2-A 508, R2-B 510, and R1-B 512. In oneembodiment of the invention, R1-A 506 and R1-B 512 are approximatelyequal to each other in resistance, and R2-A 508 and R2-B 510 are alsoapproximately equal to each other. A reference voltage, 2.5 volts in oneembodiment of the invention, is applied to node 514. The voltagedividing circuit provides a reduced voltage at the inputs of thecomparing circuit, illustrated as a 2-input operational amplifier 516.For example, where R1-A 506 and R1-B 512 are each approximately 100kilo-ohms, and R2-A 508 and R2-B 510 are each approximately 1 kilo-ohm,a voltage signal is generated at the + and −inputs of the op amp 516which is at a voltage level capable of recognition by the op amp 516. Opamp 516 compares the input values, and provides a high logic level whenthe voltage at node 518 exceeds the voltage at node 520. Alternatively,op amp 516 provides a low logic level when the voltage at node 518 islower than the voltage at node 520. Because the signals at the secondarywinding power 1 and 2 lines 502 and 504 are 180 degrees out of phase,the op amp 516 will provide a high logic level for a time correspondingto 180 degrees of the 60 Hz signal, and will provide a low logic levelfor the time corresponding to the remaining 180 degrees of the 60 Hzsignal. Therefore, a square wave on line 522 is generated having thesame frequency as the primary and secondary power signals.

The generated square wave is then fed back into a schmidt-triggerinverting device 524, which has built-in hysteresis. This invertingdevice sources or sinks current, depending on the state of the squarewave signal on line 522, through the resistance R3 526, which affectsthe voltage at node 518 and at the non-inverting input of the op amp516. This results in triggering the state of the square wave signal online 522 slightly before the zero-crossing of the 60 Hz sine wavesignal. This square wave signal is then used to trigger transitions ofthe low frequency control signal.

It should be noted that the control signal need not be modulated ontothe existing power signal. While it may be beneficial to use the powersignal as a carrier because it is already available on the powerdistribution line, the present invention is not limited to use of thepower signal as a carrier. Any time base that has long-term andshort-term stability similar to the power grid may be used to generatethe sub-carrier control signal. For example, the time base from globalpositioning system (GPS) signals could be used to generate anysub-carrier frequency desired, including a 60 Hz signal.

Referring now to FIG. 6, a waveform diagram illustrating theanticipation of the zero-crossover point is provided. As was describedin connection with FIG. 5, the primary winding power has a peak voltageof V(max), which in one embodiment of the invention is 169.7 volts for a120 volt RMS power signal. Due to the center-tapped transformer 320, thepeak voltage on the secondary winding power 1 line is V(max)/2, as isthe peak voltage on the secondary winding power 2 line. However, as canbe seen, the power 1 and power 2 lines are phase-shifted by 180 degrees.

The circuit of FIG. 5 provides for a square wave which is slightlyshifted in time with respect to the zero-crossing point of thetransformer power signal. The circuit of FIG. 5 therefore provides asquare wave having a frequency substantially equal to the frequency ofthe transformer power signal, yet shifted by an anticipation lead timeillustrated by time duration t_(ANT) 600 in FIG. 6. This time duration,set to approximately 40 microseconds in one embodiment of the invention,allows time for the low frequency signal to be modulated at or very nearto the zero-crossing points of the transformer power signal.

FIG. 7 is a diagram illustrating zero-crossover synchronization inaccordance with one embodiment of the present invention. Thezero-crossover synchronization 700 receives the transmit control signalon line 702 and the crossover sense output on line 704. The crossoversense output is a square wave having a frequency substantially equal tothe frequency of the transformer power signal, yet shifted by ananticipation lead time illustrated by time duration t_(ANT). This signalindicates when the crossover synchronize should output a valueindicative of which of the power switching transistors 426, 428, 430,432 are to be turned on and off through drivers 418, 420, 422 and 424respectively. For example, at a logic high (1) level of the transmitcontrol signal on line 702, a logic high (1) level of the crossoversense output on line 704 will cause the switch 426 to turn on. Theanticipation lead time of the crossover sense output allows the switchto be turned on slightly before another switch is turned off by thepower signal.

Referring now to FIG. 8, a schematic diagram of a power transistorcircuit 800 in accordance with one embodiment of the invention isprovided. The output power switching circuit includes four powerswitching transistors, shown in FIG. 7 as transistors 426, 428, 430 and432. FIG. 8 illustrates the relationship between two of the transistors,such as transistors 430 and 432, each of which contain a diode 802, 804that is reverse biased. When a voltage is applied to V_(CNTL) with thepolarity indicated, and the AC SOURCE on line 806 is on the positivehalf of its cycle, then transistor 430 and diode 804 will conduct in aforward-biased condition. If a voltage is applied to V_(CNTL) with thepolarity indicated, and the AC SOURCE is negative with respect to the ACOUTPUT on line 808, then transistor 432 and diode 802 will conduct in aforward-biased condition. Where V_(CNTL) is at 0 volts or at a slightlyreverse polarity, no current will flow in this circuit. This allowshalf-periods of the power signal to be inverted depending on the stateof the crossover synchronize circuit 416.

FIG. 9 is a waveform diagram illustrating one embodiment in which a lowfrequency control signal is derived using the frequency of the powersignal as a carrier signal. The 60 Hz line represents a powertransmission signal 900 on a power distribution line which can be usedas a carrier for the control signal. The 60 Hz signal is a sinusoidalsignal having a period of approximately 16.7 milliseconds. Because thezero-crossover point can be estimated using the crossover sensecircuitry of the present invention, selected half-period waveforms canbe inverted (or phase-shifted 180 degrees at the near-zero crossing).For example, the half-period waveforms 902, 904 and 906 can be invertedor phase-shifted to produce corresponding inverted half-period waveforms908, 910 and 912 respectively. Digital signal processing can be used toprovide low-pass filtering to allow only the low frequency to pass. Ascan be seen, an approximate square wave signal 914 having a frequency ofapproximately 20 Hz can be generated for the first period of the controlsignal by inverting the selected portions of the 60 Hz signal 900. Anyfrequency having a period which is an integer value of one-half of thecarrier period can be generated in a similar manner. This allows thelow-frequency control signal to be modulated onto a carrier having ahigher frequency than the control signal.

In order to determine which half-period waveforms are to be inverted,the crossover sense output and the transmit control signal are used. Aswas indicated in FIG. 7, the state of these signals determines which ofthe power switching transistors 426, 428, 430, 432 will turn on and off,which is dictated by the crossover sense output and the transmit controlsignal. Referring now to FIGS. 7 and 9, it can be seen that a high logiclevel from the crossover sense and a high logic level from the transmitcontrol signal cause switch 426 and 428 to turn on, which results in noinversion of the power signal. However, where a low logic level from thecrossover sense and a high logic level from the transmit control occur,switches 430 and 432 turn on, thereby causing an inversion of the powersignal as shown at inverted waveform 908.

In the example of FIG. 9, frequency modulation is providing the controlsignal, as can be seen by the variance between 20 Hz and 15 Hz.Subcarrier signals lasting for 1.5 periods of the 60 Hz signal are 20 Hzsignals, and subcarrier signals lasting for 2 full periods of the 60 Hzsignal are 15 Hz signals. This frequency modulation allows the controlsignal to be superimposed on the power signal at a lower frequency thanthe power signal. As will be recognized by those skilled in the art,phase modulation, or a combination of phase modulation and frequencymodulation, could also be implemented in a similar manner withoutdeparting from the scope and spirit of the invention. Therefore, theexemplary embodiment described is merely illustrative, and should not belimited to a frequency modulated system.

FIG. 10 is a functional illustration of one embodiment of a high voltageprotection unit 1000 in accordance with the present invention. Becausethe control information transmitter 1002 is connected in series with theneutral line 1004 of the power distribution line, an electrical failureof the control information transmitter 1002 may affect the powertransmission itself. While a short-circuit failure of the controlinformation transmitter 1002 to ground will not affect the powerdistribution (because a circuit loop for power transmission is stillavailable), an open-circuit condition would cause the transformerreference to ground to vanish, which would result in an unacceptablyhigh voltage to be present at the local transformer. This is a result ofthe in-series operation which causes both the ground reference and thesecondary windings (e.g., windings 318 of FIG. 3) to be modulated.Because it is the voltage differential that is used, both thetransformer windings and the ground reference may be modulated together.

In order to account for this condition, the present invention providesfor substation protection modules, such as protection unit 1000. Theseprotection modules are referred to as “anti-fuses”, because where thereis an open-circuit condition, they cause a short-circuit to ground,which is the opposite of what the operation of a standard “fuse” is.When the protection unit 1000 is activated upon recognition of anopen-circuit condition in the control information transmitter 1002, itprovides a short-circuit path from the neutral line 1004 to ground 1006,thereby maintaining a ground connection.

In one embodiment of the invention, the protection module 1000 includestwo bypass conductors 1008, 1010, which are ultimately short-circuitedtogether if the control information transmitter 1002 fails to provide acontinuous connection to ground 1012. Where the control informationtransmitter 1002 open-circuits, the voltage on the neutral line 1004causes a current to flow through bypass conductor 1008, through a devicewhich has properties such that its resistance to current drops asvoltage increases. In one embodiment of the invention, a metal oxidevaristor (MOV) 1014 is used which utilizes the nonlinear resistanceproperty of zinc oxide to form a variable resistor whose resistance tocurrent drops as voltage increases. Therefore, at relatively lowvoltages, the MOV has non-conductive insulating characteristics, whileat high voltages the MOV conducts current.

The current from the neutral line 1004 passes through the MOV 1014,through a conducting device 1016 which is used to separate the bypassconductors 1008, 1010 under normal circumstances, and back through thebypass conductor 1010. In one embodiment of the invention, theconducting device 1016 is a solder joint which holds the bypassconductors 1008, 1010 apart until the current through the MOV 1014 ishigh enough to melt the solder joint, thereby causing the tensionedbypass conductors 1008, 1010 to snap together and provide a high currentpath for the current to flow to ground 1006.

In summary, the protection unit 1000 provides a high-current path toground when the control information transmitter 1002 fails in anopen-circuit mode. As will be readily apparent to those skilled in theart from the description of the protection unit 1000, various othercomponents other than MOVs, solder joints, and the like can be similarlyused to generate the “anti-fuse” function, as the protection unit 1000of the present invention is not limited to such. It will also be readilyapparent to those skilled in the art that the device 1014 and theconducting device 1016 can be calibrated such that the bypass conductors1008, 1010 are coupled together at a desired voltage on the neutral line1004 through the selection of appropriate resistance values. Further,the precise mechanical configuration utilized is irrelevant, however thephysical and electrical properties of the bypass conductors 1008, 1010must be selected such that they can adequately carry the large currentsthat they will conduct.

FIG. 11 is a diagram illustrating one embodiment of the control signalprotocol 1100 of the present invention. The sync fields 1102, 1103 areframe synchronization fields. In one embodiment of the invention, syncfield 1102 is a predetermined number of continuous binary “1” values.Each byte is sent least significant bit first, with one start bit and nostop bits. The packet type field 1104 indicates the length of theaddress is if there is an address associated with the information, andwhat the contents of the information are. Although the exact binaryvalue corresponding to particular information may vary, one embodimentof the invention utilizes binary codes to indicate the address andinformation content as shown in Table 1 below:

TABLE 1 Types 0-3 0000 Time Broadcast 0001 Close (no address) 0010 Data0011 Options Types 4-7 0100 Time Group Address 0101 Open (8-bit address)0110 Data 0111 Options Types 8-B 1000 Time Serial Number Address 1001Open (32-bit address) 1010 Data 1011 Options Types C-F 1100 Time FSerial Number Range 1101 Open (2 32-bit addresses) 1110 Data 1111Options 0x10 File Name and Header 0x11-0xEF File Data 0xF0-0xFF Reserved

The packet type corresponding to “time” provides the time andtemperature, and may be transmitted such that the end of the stop bit isexactly at the top of the minute. In one embodiment of the invention,the temperature is a signed byte with 0.5 C degree steps, and the timeis defined in two bytes. In a first byte, bits (0-5) correspond to 0-59minutes, bit (6) corresponds to the state of a DST (daylight savingstime) flag to indicate whether the end device is in daylight savingstime, and bit (7) is for a special schedule flag which is used forholidays or other special daily schedules. A second byte uses bits (0-4)to represent hours 0-23, a GMT (Greenwich Mean Time) flag to indicatewhether the end device corresponds to GMT, a timezone offset flag toindicate whether a timezone offset has been applied to the end devicetime, and a second DST flag to indicate whether the end device includesa daylight savings time adjustment. These times and schedules allow forcontrol of particular customer devices at particular times, and accountsfor special circumstances due to holidays and other special events.

The packet type corresponding to “time” also includes the date, which,in one embodiment, includes 3 bytes of information. A first byte usesbits (0-4) to indicate the day of the month, and bits (5-7) to indicatethe day of the week. A second byte uses bits (0-3) to indicate themonth, and bits (4-7) to indicate the “season” (which can be defined),or a special schedule. A third byte uses bits (0-6) to indicate thebinary year from 0-99, and bit (7) is reserved.

The packet type corresponding to “open” is a command to select multipleend units, and “close” causes all units to be deselected. The “data”packet type corresponds to general data to be passed on to the unit. The“options” type can be used for various options, including bit rates,bandwidth and frequency.

Referring again to FIG. 11, the address field 1106 can includeinformation ranging from no bits to 2 32-bit values. For a broadcastmessage (i.e., sent to all end devices), no address needs to beprovided. For a Group Address, an 8-bit address denotes an address of aparticular group. Serial number addresses may be 1 or 2 32-bitaddresses, which addresses end units by serial number. The data field1108 provides any data to be sent, and the checksum fields 1110 up totwo different checksum values calculated in two different ways.

While the foregoing protocol is used in one embodiment of the invention,it is provided for illustrative purposes only. Various fields and binaryvalue representations can be modified without departing from the scopeand spirit of the invention, as will be readily recognized by thoseskilled in the art. Therefore, the foregoing is merely illustrative, andthe invention is not to be limited to a protocol as provided inconnection with FIG. 11 above.

The invention has been described in its presently contemplated bestmode, and it is clear that it is susceptible to various modifications,modes of operation and embodiments, all within the ability and skill ofthose skilled in the art and without the exercise of further inventiveactivity. Accordingly, what is intended to be protected by LettersPatents is set forth in the appended claims.

1. A full-duplex communications system for transmitting information,comprising: an electric power distribution line to transmit anelectrical power signal; a power distribution circuit coupled to theelectric power distribution line to provide the electrical power signalto a power consumer via the electric power distribution line; a firstinformation transmitter coupled to the power distribution circuit toprovide first information signals concurrently with the electrical powersignal to the power consumer via the electric power distribution line; afirst information receiver, coupled to a power consumer device poweredby the electrical power signal, to receive the first information signalsvia the electric power distribution line; a second informationtransmitter coupled to the power consumer device to provide secondinformation signals concurrently with the electrical power signal viathe electric power distribution line; and a second information receivercoupled to the power distribution circuit to receive the secondinformation signals via the electric power distribution line, wherebyfull duplex communication between the power distribution circuit and thepower consumer is accomplished via the electric power distribution line.2.-40. (canceled)